Control valve for variable displacement compressor

ABSTRACT

To provide a control valve for a variable displacement compressor, which is improved in slidability of a shaft that transmits a change in suction pressure to a valve element, and enhanced in controllability. In a control valve for a variable displacement compressor in which a plunger of a solenoid is divided into two, i.e. a first plunger and a second plunger, and a diaphragm is disposed therebetween for sensing suction pressure, the second plunger is held by a spring urging the second plunger in a direction away from the diaphragm, and is caused to be simply in contact with a shaft that transmits a change in the suction pressure sensed by the diaphragm to a valve element. With this construction, even when an attractive force is generated by a solenoid to move the second plunger, no couple of forces act on the shaft, and hence the shaft is prevented from being spoiled in slidability, which makes it possible to enhance controllability.

CROSS-REFERENCES TO RELATED APPLICATIONS, IF ANY

This application claims priority of Japanese Application No. 2004-298794 filed on Oct. 13, 2004 and entitled “CONTROL VALVE FOR VARIABLE DISPLACEMENT COMPRESSOR”.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a control valve for a variable displacement compressor, and more particularly to a control valve for a variable displacement compressor which is suitable for controlling refrigerant displacement of a variable displacement compressor for an automotive air conditioner.

(2) Description of the Related Art

A compressor used in a refrigeration cycle of an automotive air conditioner is driven by an engine whose rotational speed varies depending on a traveling condition of the vehicle, and hence is incapable of performing rotational speed control. For this reason, in general, a variable displacement compressor capable of changing refrigerant displacement is employed so as to obtain an adequate refrigerating capacity without being constrained by the rotational speed of the engine.

In the variable displacement compressor, in general, a wobble plate disposed within a crankcase formed gastight, such that the inclination angle thereof can be changed, is driven by the rotational motion of a rotating shaft, for performing wobbling motion, and pistons caused to perform reciprocating motion in a direction parallel to the rotating shaft by the wobbling motion of the wobble plate draw refrigerant from a suction chamber into associated cylinders, compress the refrigerant, and then discharge the same into a discharge chamber. In doing this, the inclination angle of the wobble plate can be varied by changing the pressure in the crankcase, whereby the stroke of the pistons is changed for changing the discharge amount of the refrigerant. The control valve for a variable displacement compressor controls the changing of the pressure in the crankcase.

In general, the control valve for a variable displacement compressor, which variably controls the displacement of the compressor, operates to introduce part of refrigerant at discharge pressure Pd discharged from the discharge chamber into the crankcase formed gastight, such that pressure Pc in the crankcase is controlled through control of the amount of refrigerant thus introduced. The control of the amount of introduced refrigerant is carried out e.g. by a known method of controlling the amount of introduced refrigerant according to suction pressure Ps in the suction chamber. That is, the control valve for a variable displacement compressor senses the suction pressure Ps, and controls the flow rate of refrigerant at the discharge pressure Pd introduced from the discharge chamber into the crankcase, so as to hold the suction pressure Ps at a constant level.

To this end, the control valve for a variable displacement compressor is equipped with a pressure-sensing section for sensing the suction pressure Ps, and a valve section for causing a passage leading from the suction chamber to the crankcase to open and close according to the suction pressure Ps sensed by the pressure-sensing section. Further, a type of the control valve for a variable displacement compressor which is capable of freely externally setting a value of suction pressure Ps to be assumed at the start of the variable displacement operation, is equipped with a solenoid that enables configuration of settings of the pressure-sensing section by external electric current.

By the way, conventional control valves for a variable displacement compressor which can be externally controlled include a type for control of a so-called clutchless variable displacement compressor configured such that an engine is directly connected to a rotating shaft without providing an electromagnetic clutch between the engine and the rotating shaft on which a wobble plate is fitted, for execution and inhibition of transmission of a driving force to the engine (see e.g. Japanese Unexamined Patent Publication (Kokai) No. 2000-110731 (Paragraph numbers [0010] and [0044], and FIG. 1)).

This control valve comprises a valve section causing a passage communicating between a discharge chamber and a crankcase to be opened and closed, a solenoid for generating an electromagnetic force causing the valve section to operate in the closing direction, and a pressure-sensing section for causing the valve section to operate in the opening direction as suction pressure Ps becomes lower than the atmospheric pressure, which are arranged in this order. Therefore, when the solenoid is not energized, the valve section is in a fully open state, whereby pressure Pc in the crankcase can be held at pressure close to discharge pressure Pd. This causes the wobble plate to become substantially at right angles to the rotating shaft, enabling the variable displacement compressor to operate at the minimum displacement. Thus, the refrigerant displacement can be substantially reduced to approximately zero even when the engine is directly connected to the rotating shaft, which makes it possible to eliminate the electromagnetic clutch.

However, the conventional control valve for controlling a variable displacement compressor having no use for the electromagnetic clutch is configured such that the pressure-sensing section and the valve section are arranged with the solenoid interposed therebetween, and the suction pressure Ps is introduced to the pressure-sensing section which compares the suction pressure Ps and the atmospheric pressure, via the solenoid. This necessitates the solenoid in its entirety to be accommodated within a pressure chamber, and hence components of the solenoid need to be designed with considerations given to resistance to pressure.

To eliminate this inconvenience, the present applicant has proposed a control valve for a variable displacement compressor configured such that the plunger of a solenoid is divided into a first plunger and a second plunger, and a pressure-sensing member, such as a diaphragm or a bellows, is interposed therebetween for sensing suction pressure Ps, whereby the suction pressure Ps is isolated from the atmospheric pressure in which the solenoid is disposed (Japanese Patent Application No. 2003-289581).

Further, the present applicant has proposed a control valve for a variable displacement compressor that accommodates one of the divided plungers in a vacuum container, and sealing an opening of the vacuum container with a diaphragm, whereby the diaphragm isolates suction pressure Ps from the atmospheric pressure in which the coil of a solenoid is disposed (Japanese Patent Application No. 2004-125532). Hereafter, a description will be given of details of the construction of the control valve.

FIG. 2 is a cross-sectional view showing the construction of the conventional control valve for a variable displacement compressor.

The control valve includes a valve section, as shown in an upper part of FIG. 2, which receives discharge pressure Pd from a discharge chamber of the compressor to supply controlled pressure Pc to the crankcase. The valve section comprises a valve seat 101, a valve element 102 disposed on a downstream side in opposed relation thereto, and a spring 103 urging the valve element 102 in a valve closing direction. The valve element 102 is formed integrally with a shaft 104 that is formed to have an outer diameter equal to the inner diameter of a valve hole, and is held in a body in a manner axially movable back and forth.

A solenoid is disposed, as shown in a lower part of FIG. 2. The solenoid comprises a core 106 and a first plunger 107 that are disposed within a bottomed sleeve 105, and a second plunger 108 and a coil 109 that are disposed outside the bottomed sleeve 105, with a diaphragm 110 provided between the first plunger 107 and the second plunger 108, such that the diaphragm 110 seals the open end of the bottomed sleeve 105. Within the bottomed sleeve 105, the first plunger 107 is fixed to a shaft 111 that is disposed to extend through the center of the core 106, and the shaft 111 is urged by a spring 112 in a direction of causing the first plunger 107 to be moved away from the core 106, whereby the first plunger 107 is brought into contact with an inner surface of the diaphragm 110.

Suction pressure Ps in the suction chamber of the variable displacement compressor is introduced into a space within which the second plunger 108 is disposed, and the diaphragm 110 senses the suction pressure Ps. The second plunger 108 is fixed to an end of the shaft 104 opposite to an end thereof where the valve element 102 is provided, and further is urged by a spring 113 larger in load than the spring 103 of the valve section, in a direction of moving away from the diaphragm 110. This urges the shaft 104 upward as viewed in FIG. 2, and when the control valve is not in operation, the valve section is held in a fully-open state as shown in FIG. 2. Therefore, in this state, even if the rotating shaft of the compressor is driven by the engine for rotation, the compressor is operated at the minimum displacement.

Now, if control current is supplied to the coil 109 of the solenoid, the first plunger 107 and the second plunger 108 are magnetically coupled to each other with the diaphragm interposed therebetween so as to behave as one plunger. At this time, the axial positions of the first plunger 107 and the second plunger 108 determine a valve lift of the valve section, and the valve lift is set according to the control current supplied to the coil 109. On the other hand, the diaphragm 110 receives the suction pressure PS, and hence is axially displaced according to the suction pressure Ps. The displacement of the diaphragm is transmitted to the valve element 102 via the second plunger 108 and the shaft 104.

Therefore, the control valve for a variable displacement compressor introduces refrigerant at pressure Pc into the crankcase by controlling the flow of refrigerant at discharge pressure Pd to a flow rate dependent on the control current supplied to the coil 109. This causes the compressor to operate at displacement dependent on the control current. In this state, if the suction pressure Ps rises, the diaphragm 110 is displaced downward as viewed in FIG. 2, while if the suction pressure Ps drops, the diaphragm 110 is displaced upward as viewed in FIG. 2. According to the displacement of the diaphragm 110, the valve lift of the valve section is varied to thereby adjust the pressure Pc in the crankcase, and hence after all, the compressor has its displacement controlled such that suction pressure Ps becomes equal to a value set by the solenoid.

However, in the control valve described above, the shaft formed integrally with the valve element also has the function of guiding the second plunger. Therefore, when the second plunger is axially moved by an attractive force produced on the second plunger by the solenoid, the second plunger is tilted depending on the state of the spring axially urging the second plunger, so that a couple of forces act on the shaft held in the body, to markedly spoil the axial slidability of the shaft, so that the valve element becomes incapable of moving smoothly.

SUMMARY OF THE INVENTION

The present invention has been made in view of this problem, and an object thereof is to provide a control valve for a variable displacement compressor which is improved in slidability of a shaft that transmits a change in suction pressure to a valve element and is enhanced in controllability.

To solve the above problem, the present invention provides a control valve for a variable displacement compressor in which a plunger of a solenoid is divided into a first plunger and a second plunger, and a pressure-sensing member is disposed between the first plunger and the second plunger, for sensing suction pressure, the second plunger transmitting a change in the suction pressure sensed by the pressure-sensing member to a valve element via a shaft, wherein the second plunger is held by a spring that urges the second plunger in a direction away from the pressure-sensing member, and is caused to be in contact with the shaft.

The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a central longitudinal cross-sectional view of the construction of a control valve for a variable displacement compressor of the present invention.

FIG. 2 is a cross-sectional view showing of the construction of a conventional control valve for a variable displacement compressor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a central longitudinal cross-sectional view of the construction of a control valve for a variable displacement compressor, according to the present invention.

This control valve has a valve section provided as shown in an upper part of FIG. 1. The valve section includes a body 11 formed with a side opening which communicates with a discharge chamber of the variable displacement compressor to form a port 12 for receiving discharge pressure Pd from the discharge chamber. The port 12 has a strainer 13 fixed to the periphery thereof. The port 12 for receiving the discharge pressure Pd communicates with a port 14 opening in the top of the body 11, via a refrigerant passage formed through the inside of the body 11. The port 14 communicates with the crankcase of the variable displacement compressor so as to deliver controlled pressure Pc to the crankcase.

In the refrigerant passage via which the port 12 and the port 14 are communicated through the body 11, a valve seat 15 is formed integrally with the body 11. In opposed relation to a side of the valve seat 15, from which the pressure Pc is delivered, a valve element 16 is axially disposed in a manner movable to and away from the valve seat 15. The valve element 16 is formed integrally with a shaft 17 which extends downward as viewed in the figure through a valve hole such that it is axially movably held by the body 11. The discharge pressure Pd from the discharge chamber is introduced into a small-diameter portion which connects between the valve element 16 and the shaft 17. The outer diameter of the shaft 17 is set to be equal to the inner diameter of the valve hole forming the valve seat 15 such that the pressure-receiving area of the valve element 16 is equal to that of the shaft 17. This causes a force of the discharge pressure Pd which acts on the valve element 16 in the upward direction as viewed in FIG. 1 to be cancelled out by a force acting on the shaft 17 in the downward direction as viewed in FIG. 1, so as to prevent the control of the valve section from being adversely affected by the discharge pressure Pd which is high in pressure level.

The valve element 16 is urged by a spring 18 in the valve closing direction, and load of the spring 18 is adjusted by an adjustment screw 19 screwed into the port 14.

Further, a port 20 communicating with a suction chamber of the variable displacement compressor to receive suction pressure Ps is formed in a lower portion of the body 11 as viewed in FIG. 1.

The lower end of the body 11 is rigidly press-fitted in a body 21 of a magnetic material forming a part of the solenoid. Arranged within the body 21 is a second plunger 22 as one of divided plungers of the solenoid. The second plunger 22 has a hole formed in the center of an upper end face thereof as viewed in FIG. 1 such that the hole has an inner diameter larger than the outer diameter of the shaft 17. The shaft 17 which is held by the body 11 without almost any clearance in a manner axially movable back and forth has a lower end face thereof brought into contact with the bottom of the hole. The lower end face of the shaft 17 is formed to be arcuate in cross-section, which prevents a couple of forces from being generated on the shaft 17 by vertical motions of the second plunger 22 even when the shaft 17 is not in contact with the bottom of the hole precisely at right angles. The second plunger 22 is also formed to have a T shape in cross-section, and a lower surface of a flange 23 thereof as viewed in FIG. 1 is opposed to an upper surface of the body 21 as viewed in FIG. 1. This causes an axial attractive force to be generated between the opposed surfaces of the flange 23 and the body 21 to thereby assisting the valve section in promptly moving in the valve closing direction. Further, the second plunger 22 is urged by a spring 24 disposed between the same and a stepped portion formed inside the body 21, upward as viewed in FIG. 1. The spring 24 has a larger load than that of the spring 18 urging the valve element 16 in the valve closing direction. Therefore, when the solenoid is not energized, the second plunger 22 can push the shaft 17 upward until the shaft 17 is brought into contact with the ceiling of a chamber communicating with the port 20, and hold the valve element 16 in its fully open position. The spring 24 also holds a part of the second plunger 22 lower than the flange 23 thereof, whereby the spring 24 has the function of guiding the second plunger 22.

Below the second plunger 22 as viewed in FIG. 1, there are arranged the pressure-sensing section and the remaining component parts of the solenoid. More specifically, below the second plunger 22 as viewed in FIG. 1, there is disposed an assembly that is formed by accommodating a first plunger 26 as the other of divided plungers of the solenoid, a core 27, and a spring 28, in the bottomed sleeve 25 forming the vacuum container, and sealing the opening of the bottomed sleeve 25 with a metal diaphragm 29, and outside the bottomed sleeve 25, there are arranged a coil 30, and a case 31 formed integrally with the body 21 and a handle 32 which constitute a yoke for forming a magnetic circuit.

In the bottomed sleeve 25, the core 27 is rigidly press-fitted and the first plunger 26 is disposed on a side of the core 27 toward the valve section in a manner axially movable back and forth. The first plunger 26 is rigidly press-fitted on one end of a shaft 33 axially extending in the center of the core 27, and the other end of the shaft 33 is supported by a bearing 34 slidably disposed in the core 27. A stop ring 35 is fitted on an intermediate portion of the shaft 33, and a spring-receiving member 36 is provided such that the upward movement thereof as viewed in FIG. 1 is restricted by the stop ring 35. The spring 28 is interposed between the spring-receiving member 36 and the bearing 34. The first plunger 26 is urged by the spring 28 via the shaft 33 in a direction away from the core 27. It should be noted that the bottom of the bottomed sleeve 25 is pushed to be deformed inward, whereby the axial position of the bearing 34 is changed to adjust the load of the spring 28. Thus, the set point of the control valve is adjusted.

The bottomed sleeve 25 accommodating the first plunger 26 and the core 27 as described above is sealed by welding the diaphragm 29 to a flange portion formed on the open end of the bottomed sleeve 25, whereby the gastight assembly is formed such that the inside thereof is maintained under vacuum.

In the construction described above, the body 21, the case 31, and the handle 32 are formed of magnetic substances to serve as the yoke of the magnetic circuit of the solenoid. Magnetic lines of force generated by the coil 30 pass through the magnetic circuit formed by the case 31, the body 21, the second plunger 22, the first plunger 26, the core 27, and the handle 32.

FIG. 1 shows a state of the control valve for a variable displacement compressor, in which the solenoid is not energized and the suction pressure Ps is high, i.e. a state in which the air conditioner is not operating. Since the suction pressure Ps is high, the diaphragm 29 is displaced downward as viewed in FIG. 1 against the load of the spring 28 to bring the first plunger 26 into contact with the core 27. On the other hand, the second plunger 22 is urged upward as viewed in FIG. 1, by the spring 24 such that it is moved away from the diaphragm 29, and hence urges the valve element 16 toward its fully open position via the shaft 17. Therefore, even when the rotating shaft of the variable displacement compressor is being driven for rotation by the engine in the above state, the variable displacement compressor is operated at the minimum displacement.

Now, when the maximum control current is supplied to the coil 30 of the solenoid, as in the case of the start of the automotive air conditioner, the first plunger 26 has been pressed downward as viewed in FIG. 1 by the high suction pressure Ps to be brought into contact with the core 27, so that even if the first plunger 26 is attracted by the core 27, it remains in the same position. Therefore, in this case, the first plunger 26 and the core 27 behave as if they were a fixed core, so that the first plunger 26 attracts the second plunger 22 via the diaphragm 29 against the urging force of the spring 24. The second plunger 22 is attracted to be brought into contact with the diaphragm 29, whereby the second plunger 22 is moved downward, as viewed in FIG. 1. This allows the spring 18 to push the valve element 16 downward, thereby causing the valve element 16 to be seated on the valve seat 15, to fully close the valve section. This blocks off the passage extending from the discharge chamber to the crankcase, so that the variable displacement compressor is promptly shifted into the operation at the maximum displacement. At this time, the second plunger 22 is only in contact with the shaft 17 but not constrained thereby, so that even when the second plunger 22 is about to be moved in a tilted state depending on the condition of the spring 24 guiding the second plunger 22, no couple of forces act on the shaft 17 and hence the axial slidability of the shaft 17 is not spoiled.

When the variable displacement compressor continues to operate at the maximum displacement to make the suction pressure Ps of the suction chamber low enough, the diaphragm 29 senses the suction pressure Ps and attempts to move upward, as viewed in FIG. 1. At this time, if the control current supplied to the coil 30 of the solenoid is decreased according to the set temperature of the air conditioner, the second plunger 22 and the first plunger 26 in the attracted state move in unison upward, as viewed in FIG. 1 to respective positions where the suction pressure Ps, the loads of the springs 18, 24, and 28, and the attractive force of the solenoid are balanced. This causes the valve element 16 to be pushed upward by the second plunger 22 to move away from the valve seat 15, thereby being set to a predetermined valve lift. Therefore, refrigerant at the discharge pressure Pd is introduced into the crankcase at a flow rate controlled to a value dependent on the valve lift, whereby the variable displacement compressor is shifted to an operation with the displacement corresponding to the control current.

Then, when the control current supplied to the coil 30 of the solenoid is constant, the diaphragm 29 senses the suction pressure Ps as an absolute pressure to thereby control the valve lift of the valve section. For example, when the refrigeration load increases to make the suction pressure Ps high, the first plunger 26 is displaced downward as viewed in FIG. 1, so that the valve element 16 is also moved downward to decrease the valve lift of the valve section, causing the variable displacement compressor to operate in a direction of increasing the displacement. On the other hand, when the refrigeration load decreases to make the suction pressure Ps low, the first plunger 26 is displaced upward as viewed in FIG. 1 to increase the valve lift of the valve section, causing the variable displacement compressor to operate in a direction of decreasing the displacement. Thus, the control valve controls the displacement of the variable displacement compressor such that the suction pressure Ps becomes equal to a value set by the solenoid.

The preferred embodiment of the present invention has been described heretofore, but the present invention is by no means limited to the preferred embodiment. For example, although in the above-described embodiment, the first plunger 26 is accommodated in the vacuum container and the suction pressure Ps is sensed in terms of absolute pressure, this is not limitative, but the present invention is also applicable to a type of the variable displacement compressor in which a section accommodating the first plunger 26 is made open to the atmospheric pressure to thereby compare the suction pressure Ps and the atmospheric pressure. Furthermore, although the pressure-sensing section is formed by a diaphragm in the above-described embodiment, it may be formed by a bellows.

The control valve for a variable displacement compressor according to the present invention is configured such that a shaft for transmitting a change in suction pressure to a valve element does not have the function of guiding a second plunger, and hence even if the second plunger is tilted when the second plunger is axially moved by an attractive force generated by a solenoid, the tilting of the shaft is prevented from having influence on the shaft, which has the advantage of enhancing the controllability.

The foregoing is considered as illustrative only of the principles of the present invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and applications shown and described, and accordingly, all suitable modifications and equivalents may be regarded as falling within the scope of the invention in the appended claims and their equivalents. 

1. A control valve for a variable displacement compressor in which a plunger of a solenoid is divided into a first plunger and a second plunger, and a pressure-sensing member is disposed between the first plunger and the second plunger, for sensing suction pressure, the second plunger transmitting a change in the suction pressure sensed by the pressure-sensing member to a valve element via a shaft, wherein the second plunger is held by a spring that urges the second plunger in a direction away from the pressure-sensing member, and is caused to be in contact with the shaft.
 2. The control valve according to claim 1, wherein the second plunger has a hole formed in a center of a surface thereof on a side opposed to the shaft, the hole having an inner diameter larger than an outer diameter of the shaft, and an end face of the shaft is in contact with a bottom of the hole.
 3. The control valve according to claim 2, wherein the end face of the shaft in contact with the bottom of the hole is formed to be arcuate in cross section. 